Shelf



FIG. 1 is a top right perspective view of a shelf showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a right side elevational view thereof, the left side elevational view being a mirror image; and,

FIG. 5 is a rear elevational view thereof. 

The ornamental design for a shelf, as shown and described. 